Condensed soluble hydrogensilsesquioxane resin

ABSTRACT

Hydrogensilsesquioxane, free of hydroxyl content, of the general formula (HSiO3/2)n where n is an even integer of 10 or more, is disclosed. The condensed hydrogensilsesquioxane is prepared by condensation of trichloro-, trimethoxy- or triacetoxysilanes in a sulfuric acid medium. A specific example is (HSiO3/2)2 where n has an average value of 20 or more. This material is a resinous polymer which contains small amounts of volatile oligomers and is useful as a protective coating.

United States Patent [72] Inventors Warde T. Collins;

Cecil L. Frye, both of Midland, Mich. [211 App]. No. 773,314 [22] Filed Nov. 4,1968 [45 Patented Oct. 26, 1971 [73] Assignee Dow Corning Corporation Midland, Mich.

i541 CONDENSED SOLUBLE HYDROGENSILSESQUIOXANE RESIN 9 Claims, No Drawings [52] US. Cl 23/366, 117/161, 260/37, 260/46.5, 260/448.2, 260/825 [51] Int. Cl C0lh 33/04 [50] Field of Search 260/46.5, 46.5 1-1, 448.2 H; 23/366 [56] References Cited UNITED STATES PATENTS 2,827,474 3/1958 Kress 260/4482 2,832,794 4/1958 Gordon 260/448.2 2,844,435 7/1958 Wagner et a1 23/366 2,901,460 8/1959 Boldebuck 260/46.5

OTHER REFERENCES Muller et al., J. Prakt. Chem. (4) 9, 71 (1959) pp. 7l 74 TH .189

Primary Examiner-Donald E. Czaja Assistant ExaminerM. I. Marquis Att0rneysRobert F. Fleming, Jr., Laurence R. Hobey and Harry D. Dingman ABSTRACT: l-lydrogensilsesquioxane, free of hydroxyl content, of the general formula (l-lSiO3/2), where n is an even integer of 10 or more, is disclosed. The condensed hydrogensilsesquioxane is prepared by condensation of trichl0ro-, trimethoxyor triacetoxysilanes in a sulfuric acid medium. A specific example is (HSiO3/2) where n has an average value of 20 or more. This material is a resinous polymer which contains small amounts of volatile oligomers and is useful as a protective coating.

CONDENSED SOLUBLE HYDROGENSILSESQUHOXANE RESIN This invention relates to completely condensed hydrogensilsesquioxane. In one aspect, the invention relates to a method of preparing hydrogensilsesquioxane which is free of hydroxyl content.

Hydrogensilsesquioxane is known in the art. The prior art is directed to hydrogensilsesquioxane which is not fully condensed, i.e., that which contains at least some end-blocking hydroxyl or alkoxyl groups. Because of this hydroxyl content, the known hydrogensilsesquioxane is susceptible to further condensation and readily forms an insoluble gel when it is attempted to volatize solvents, such as benzene or ether. U. S. Pat. No. 2,901,460 sets forth the state of the art with respect to gelation during hydrolysis reactions.

There in one report of the production of condensed octameric hydrogensilsesquioxane by Muller et al., J. Prakt. Chem., (4) 9 71 (1959). This compound, (HSiO was recovered in less than 1 percent yield as the unexpected product of the reaction of trichlorosilane and hexamethyldisiloxane in 80 percent sulfuric acid. A detailed discussion of the cubical stmcture of the octamer is given by K. Larsson in Arkiv. Chem, 16 215, (1960).

It is an object of the invention to provide completely condensed hydrogensilsesquioxane of relatively high molecular weight.

Another object of the invention is to provide a method of obtaining high yields of completely condensed hydrogensilsesquroxane.

These and other objects of the invention will be apparent to one skilled in the art upon consideration of the following specification and appended claims.

According to the invention there is provided a composition consisting of a hydroxyl-free polymer of the formula (H- SiC where n is an even integer having an average value of or more.

The hydroxyl-free or completely condensed polymer of the invention is a highly cyclicized material which is soluble in nonpolar organic solvents, such as benzene and hexane. The polymers of the invention include volatile species and higher molecular weight nonvolatile soluble resins. The polymers which are made up of 18 or more hydrogensilsesquioxane units are the nonvolatile resins and are especially useful as coating materials since they can be applied to a substrate from a solution with subsequent evaporation of the solvent to form a resinous film. They can be used to render textiles water repellent and to protect metal surfaces from corrosion. The (llSiO,-,, compounds can also be added to siloxane elastomers as cross-linking agents. These compounds are contrasted with the prior art hydrogensilsesquioxanes which are not condensed and form gels.

Further, in accordance with the invention, there is provided a method of producing completely condensed hydrogensilsesquioxanes comprising the steps of:

a. adding a solution of trichloro-, trimethoxy-, or triacetoxysilanes in an hydrocarbon solvent to a two-phase reaction medium comprising concentrated sulfuric acid and an aromatic hydrocarbon while mixing the two-phase acid medium to effect condensation of the silanes;

b. washing the reaction mixture with water until substantially neutral;

c. recovering condensed hydrogensilsesquioxanes by evaporation of the hydrocarbon solvent and aromatic hydrocarbon.

Trichlorosilane is the preferred reactant because of its ready availability. Other suitable silanes include triacetoxysilane and trimethoxysilane.

Practice of the above method results in very high, sometimes quantitative, yields of condensed hydrogensilsesquioxane. The method may be practiced in a batch manner or as a continuous reaction. A continuous column reaction-separation technique with recovery and recycle of the acid media is a preferred embodiment of the method.

in order to obtain nearly quantitative yields of the completely condensed polymer, certain factors are critical in the practice of the method. The silane must be in a relatively dilute solution before it is added to the acid medium. Solutions of about 10 weight percent silane in the hydrocarbon solvent are preferred since this solution provides the maximum yield while using the least amount of solvent. Any suitable hydrocarbon which is a solvent for the silane reactant can be used. Exemplary of such solvents are saturated aliphatic hydrocarbons, such as n-pentane, hexane, n-heptane, and isooctane; aromatic and cycloaliphatic hydrocarbons, such as cyclohexane, benzene, toluene and :xylene; and halogennated aliphatic and aromatic hydrocarbons, such as trichloroethylene, perchloroethylene, bromobenzene and chlorobenzene.

The rate of addition of the silane solution to the acid medium is also important in obtaining high yields. The rate of addition must be sufficiently slow to avoid any substantial gelation of part of the product. The exact addition rate depends upon the volume of the acid medium and the degree to which the media is mixed. Stirring or other mechanical mixing of the reactants and the two-phase acidl media prevents phase separation of the medium and aids in the transport of the silane to the acid, giving rapid dilution of silane in acid phase.

The two-phase reaction medium comprises concentrated sulfuric acid and an aromatic hydrocarbon. While the acid is described as concentrated," this is meant to include sulfuric acid which contains up to 10 percent water. The industrial grade acid can be utilized in the process. The second component of the two-phase reaction medium is an aromatic hydrocarbon, such as benzene, toluene, xylene and the like. Benzene and toluene are preferred because of their low boiling points which allow them to be easily distilled from the product.

Although the exact reaction mechanism has not been determined, the low concentration of water needed for hydrolysis of the silanes may arise from sulfonation of the aromatic hydrocarbon as shown by the following reaction:

There is a partial hydrolysis of a portion of the silanes to form silanols, l-lSiXAOH), ll-lSiX(0H) or l-lSi(0H) with the evolution of l-IX. The silanes also presumably react initially with the acid phase to form the silylsulfate, silylbisulfate or silylaromaticsulfonate species. These species are believed to condense with the silanol to produce siloxane linkages while regenerating the sulfuric and/or .arylsulfonic acid. The dehydrating properties of sulfuric acid also aid in preventing the fonnation of partial condensates. This mechanism provides for complete condensation to the silsequioxane and precludes the presence of silanol substituents in the polymer product.

In accordance with this explanation, the ratio of sulfuric acid to aromatic hydrocarbon in the two-phase medium is not critical and can be varied with wide limits, so long as a sufficient quantity of water is being generated to react with the silanes added to the medium.

In one embodiment of the method, a quantity of fuming sulfuric acid is added to the reaction medium to consume the bulk of water present in the concentrated sulfuric acid. The arylsulfonic acid can also be added to the reaction medium. When the acid phase is reused or recycled, it has been found that the reaction rate is slower. This difficulty is overcome by the addition of a small quantity of water to the acid phase during recycle or before reuse. This results in the generation of sulfuric acid and prevents the attainment of equilibrium conditions.

The reaction product is a mixture ofvolatile oligomeric species, i.e., (HSiO Q and a nonvolatile resinous polymer. The ratio of volatile oligomers to nonvolatile polymer is dependent upon reaction conditions, such as silane addition rate, sulfuric acid concentration and the like. The reaction conditions also affect the relative amounts of the individual oligomeric species in the volatile fraction of the product. The production of octameric hydrogensilsesquioxane is generally low, for example, less than 1 percent of the product. It is believed that the octamer is not as resistant to acid rearrangement as are the other species and that after a period of time in the strong acid medium, the octamer is rearranged to higher cyclicized species, such as (HSiO,,,),,. If desired, the proportion of lower molecular weight species in the volatile fraction can be increased by diluting the sulfuric acid with glacial acetic acid. The change in the nature of the product is attributed to the greater effective dilution of the condensing silane and dilution of the sulfuric acid thereby decreasing the acid rearrangement of the octamer.

The following examples are considered illustrative of the invention and are not to be construed as unduly limiting the invention which is properly set forth in the appended claims.

EXAMPLE 1 A solution of 12.7 grams of trichlorosilane in 150 milliliters of benzene was slowly added to a rapidly stirred mixture of 200 milliliters of benzene, 80.3 grams of concentrated sulfuric acid (95-98% "280), and 60.4 grams of fuming sulfuric acid (15% S0,). The silane addition to the acid medium was carried out over a 6.5 hour period. After completion of the addition, the reaction mixture was poured into a separatory funnel and the acid phase was removed. The benzene phase was washed until neutral to the acid test paper.

During the washing step, difficulty was encountered because of emulsion formation. Benzenesulfonic acid was formed in the reaction mixture and it is believed that the material was acting as a surfactant. This difficulty was overcome by washing with 50 percent sulfuric acid, then with distilled water.

After washing until neutral, the benzene solution was filtered to yield 0.1 gram of insoluble material. The benzene solution was then evaporated to dryness, leaving 4.9 grams 97.8 percent yield) of solid resinous polymer, (HSi;,,,),,. This material did not gel during this process and was completely soluble in hexane.

Equivalent results were obtained when this method was performed in a continuous manner using toluene as the aromatic hydrocarbon phase of the reaction medium.

EXAMPLE 2 Several samples of condensed hydrogensilsesquioxane were prepared by the method of example 1. The volatile oligomeric fraction ranged from 9 to 27 percent of the total product. The individual volatile components of this fraction were separated from one another by vapor phase chromatography. A lO-foot chromatographic column, packed with 20 percent trifluoropropyl-methylsiloxane on acid-washed Chromasorb packing material (80-100 mesh), was used. A typical distribution of volatile species was as follows:

Weight of Volatile Oligomer Molecular Weight Volatile Fraction (HSiO,,,),, 530 4.2 ("Sleuths 636 43.2 ("850 m 742 36.8 siomhl 848 13.5

EXAMPLE 3 A mixture of 2,260 grams of the sulfuric acid phase, recovered from an earlier preparation of this type, and one liter of benzene were added to a 5-liter flask. The contents of the flask were stirred vigorously while adding a solution of 136.5 grams of trichlorosilane in 1.5 liter of benzene. The solution was added to the flask by use of a pressure-compensating dropping funnel under a nitrogen atmosphere. Total addition time was 10.5 hours.

After completion of the addition, the reaction mixture was transferred to a separatory funnel and the acid phase was removed. The benzene phase was then washed with water until neutral to acid test paper. The solution was dried with sodium sulfate and evacuated to dryness. The reacted material was then redissolved in hexane and the solution was evaporated to dryness to yield 53.9 grams of soluble fully condensed hydrogensilsesquioxane.

A sample of the product was found to contain 15.9 percent volatile material by sublimation. The distribution of the volatile species was determined by GLC peak area percentages to be as follows:

("Sl an" 12.4% (HSiO,,,),, 48.8% (HSi0,,,),, 35.7%

(HSiO,,,,, 31%

EXAMPLE 4 A solution of 10 milliliters of HSiCl; (0.1 mole) in 150 milliliters of benzene was added over a 5-hour period to a stirred reaction medium of 260 grams of concentrated (95-98%) H SO,, 200 grams of fuming H 50, (IS-18% S0,) and 200 milliliters of benzene. After 24 hours the benzene phase was washed free of acid and evacuated to dryness. Four grams (75.5% yield) of hexane-soluble product were recovered.

Analysis: Calculated for (HSiO C., O; H, 1.89; Si, 52.8. Found: C., 1.52; H, 1.73; Si, 49.2. There was no detectable amount of silanol observed by infrared spectroscopy. The minor carbon content (1.52 percent) indicated the presence of a trace of benzene in the product.

EXAMPLE 5 A solution of 12.9 grams of HSi (OCl-l (0.106 moles) in 150 milliliters of benzene was added over a 5-hour period was added to a stirred mixture of 80.2 grams of concentrated (95-98%) H 59.8 grams of fuming H 80 (15-1 8% S0,) and 200 milliliters of benzene. After 72 hours, the benzene phase was washed until neutral, filtered and evacuated to dryness to obtain 3.6 grams (68 percent yield) of hexane-soluble hydrogensilsesquioxane.

EXAMPLE 6 A solution of 10 milliliters of HSiCl (0.1 mole) in 150 milliliters of benzene was added dropwise over a 3.75-hour period to a stirred mixture of 170 grams of concentrated (-98%) H 80 35 grams of benzenesulfonic acid and 200 milliliters of benzene. The benzene phase was washed until neutral and evaporated to dryness to obtain 4.0 grams (75.5% yield) of soluble hydrogensilsesquioxane.

EXAMPLE 7 For purposes of comparison, a solution of 10 milliliters of l-lSiCl; in milliliters of benzene was added to a stirred mixture of 177 grams of concentrated (95-98%) H 80, and 200 milliliters of benzene over a 5.5-hour period. Neither fuming sulfuric nor benzenesulfonic acid were added to the reaction medium. After washing and evaporating the benzene, 1.8 grams (34 percent yield) of soluble hydrogensilsesquioxane were recovered. This example demonstrates that the process is operable without the addition of fuming sulfuric or arylsulfonic acid to the two-phase reaction medium. It also demonthese materials.

EXAMPLE 8 A solution of milliliters (0.1 mole) of HSiCl in 150 miladded in an amount sufficient to provide the 1:1 ratio of (H- SiO I SiOH in the blend. The blend was then corrpounded with the same amounts of filler and catalyst as used in the above-described preparation to form a second 5 elastomer. This second elastomer was cured and tested in the liliters of benzene was added over a 4-hour period to a stirred same manner as the first. Test results are tabulated below:

Elonga- Tear 150% Curing Shore A" Tensile tion, strength, modulus Elastomer time durometor (p.s.i.) percent lfi/in. (p.s.i.) 1 {1 week 52 940 350 70 360 lmonth... 52 925 305 460 2 1 week. 37 675 360 134 220 1 month... 46 730 300 95 340 reaction medium of 80 grams of concentrated (95-98%) This example demonstrates the effectiveness of (HSiO H 80 60 grams of fuming sulfuric acid (15% S0 200 milin providing cross-linking sites in silicone elastomer formulaliliters of glacial acetic acid and 200 milliliters of benzene. The tions. I addition of silane reactant to the reaction medium was made Rhasohhble '"Q Vanahohs are wlthm the scope of ft cooling the medium to room temperature. the invention which sets forth novel condensed hydrogensil- Analysis of the product, (HSiO by GLC h d three sesquioxane compounds and a method for producing the volatile species; (HSiO (HSiO and (HSiO to same- I be present in an area ratio of 22:]. This example demon- Thatwh'ch5F!a'med1s5 strates the effect of glacial acetic acid in increasing the con- A Composmoh of cohslstmg f a hydroxyl-ftee tent of lower molecular weight oligomers in the volatile spe- 25 hf of the formula where n even f cies ofthe reaction product having a value of 10 or more, said. polymer being soluble in hexane. EXAMPLE 9 2. The composition of claim 1 wherein n has a value of l 8 or When a 5 weight percent hexane solution of the nonvolatile a furthgr chafractenzd as a nonvolatile resm' resin, (HSiO n being 18 or more, is brushed onto the sur- 3O A me} 0d producmg.hgxanfisohibla fully condensed face of a titanium panel, the adhesion of alkaline iron oxide hydrogensflsesquioxane conslstmg essenuauy ofthe of: filled-fluorosilicone sealants to the surface is greatly improved @actmg Selected mm the ghoup cons.lsung of over adhesion of the sealant to an unprimed titanium surface. mdflorosllane. h w and macetoxysllane by adding a solution of said silane in a hydrocarbon solvent EXAMPLE 10 to a two-phase reaction medium consisting essentially of concentrated sulfuric acid and an aromatic hydrocarbon, h hydljogehsllseqhloxahe was evaluated In a slhcone while mixing said reaction medium, to effect hydrolysis hydride cufmg y m The 3l2)n resin was disshlved in and condensation of the silanes therein to hydroxyl-free tPhlehe h reacted with a sllahol Fhdhlocked p y y hydrogensilsesquioxane, said addition of silanes being at a shoxahe the p h of nickel Catalyst to form 40 rate sufficiently slow to avoid any substantial gelation of elastomer base. Specifically, mixture of 7.42 grams of (H- the reacnon product; 3/2)" 117 grams of toluene and grams of Nlclz was b. washing the reaction mixture until substantially neutral; heated at 1 10 C. for 1 hour; after which, 1 [0 grams of silanol and end-blocked PQ Y Y 2 fluid were c. recovering condensed hydrogensilsesquioxane by added to the m xture. These quantities of siloxane fluid and evaporation fth Solvent and aromatic hydrocarbon, (HS'O3/2)" Provided a (SICK/2)" /ES1OH of 1:1 in the 41. The method of claim 3 wherein said aromatic hydrocarreaction mixture. The reaction was carried out at l l0 C. for 3 be is benzene 0r toluena {g gfg fii fi gsfi iffl fgi gf of Solvent by 5. The method of claim 3 wherein said reaction medium Thegproduct a 3 600 cs fluid i partially consists essentially of concentrated sulfuric acid, fuming sulblocked with Sill groups. Analysis showed a SiH content furic acid and benzene' 0t0.088 percent anda ESiOH content ofou percent. 6. The method of claim 3 wherein said reaction med1um one hundred parts by weight of the product were consists essentially of concentrated sulfuric acid, an arylsulpounded with 30 parts by weight of silica filler and 1 part by fomc h 'fm hh 9 m? X weight of dibutyltin dilaurate to form a first elastomer. This The method of Claim 3 Wherem Shane reactant elastomer was allowed to cure at room temperature and 50 percent relative humidity. The properties of samples of the elastomer were determined after 1 week and 1 month of curing.

For purposes of comparison, particles of the (HSiO resin were blended with the above-described 6 polydimethysiloxane fluid on a three-roll mill. The resin was 8. The method of claim 3 wherein said silane solution contains not more than about percent by weight silane.

9. The method of claim 3 wherein said silane is l-lSiCl said hydrocarbon solvent is benzene and said reaction mixture consists essentially of concentrated sulfuric acid, fuming sulfuric acid and benzene. 

2. The composition of claim 1 wherein n has a value of 18 or more, further characterized as a nonvolatile resin.
 3. A method of producing hexane-soluble, fully condensed hydrogensilsesquioxane consisting essentially of the steps of: a. reacting a silane, selected from the group consisting of trichlorosilane, trimethoxysilane and triacetoxysilane, by adding a solution of said silane in a hydrocarbon solvent to a two-phase reaction medium consisting essentially of concentrated sulfuric acid and an aromatic hydrocarbon, while mixing said reaction medium, to effect hydrolysis and condensation of the silanes therein to hydroxyl-free hydrogensilsesquioxane, said addition of silanes being at a rate sufficiently slow to avoid any substantial gelation of the reaction product; b. washing the reaction mixture until substantially neutral; and c. recovering condensed hydrogensilsesquioxane by evaporation of the solvent and aromatic hydrocarbon.
 4. The method of claim 3 wherein said aromatic hydrocarbon is benzene or toluene.
 5. The method of claim 3 wherein said reaction medium consists essentially of concentrated sulfuric acid, fuming sulfuric acid, and benzene.
 6. The method of claim 3 wherein said reaction medium consists essentially of concentrated sulfuric acid, an arylsulfonic acid and an aromatic hydrocarbon.
 7. The method of claim 3 wherein said silane reactant is HSiCl3.
 8. The method of claim 3 wherein said silane solution contains not more than about 10 percent by weight silane.
 9. The method of claim 3 wherein said silane is HSiCl3 , said hydrocarbon solvent is benzene and said reaction mixture consists essentially of concentrated sulfuric acid, fuming sulfuric acid and benzene. 